Enable hla_serial for TI ICDI devices

Used jtag_libusb_open from libusb_helper.h instead of
libusb_open_device_with_vid_pid to get device handle,
as well as managing context, i.e. similar to stlink_usb.
Direct calls to libusb1 are left in for the moment.

(When this Gerrit revision was originally created,
the jtag_libusb_ wrappers did not return error conditions.)

Tested w/ a TM4C123GXL board

Change-Id: I71e9a366356c125444d4813e58ddd9b6c6498bf0
Signed-off-by: John Pham <jhnphm@gmail.com>
Signed-off-by: Matthew Trescott <matthewtrescott@gmail.com>
Reviewed-on: http://openocd.zylin.com/2527
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>